It is general that vehicles such as an automobile include airbag devices that absorb impacts applied to occupants in the case of an emergency such as a collision or sudden deceleration by inflating and deploying airbags in the cabins of the vehicles. Different types of such airbag devices have been developed and employed, including a driver airbag device provided in a steering, a passenger airbag device provided in the instrument panel, a side airbag device provided in a side face of the vehicle or in a seat, a curtain airbag device provided in an upper part of a door, a knee airbag device intended for the knees of the occupant, and a pedestrian airbag device provided below the hood.
In general, the above airbag devices each include an airbag that is normally folded and is inflated and deployed in the case of an emergency, an inflator for supplying gas into the airbag, and a retainer for retaining the airbag and the inflator. Such an airbag may be provided with a tether that regulates the shape of inflation and deployment of the airbag or controls the opening and closing of a vent hole, for example (see Japanese Unexamined Patent Application Publication No. 2006-341740, Japanese Unexamined Patent Application Publication No. 07-277124, Japanese Patent No. 2677951, Japanese Unexamined Patent Application Publication No. 2003-095047, Japanese Patent No. 4666059, for example).
An airbag device disclosed by Japenese Unexamined Patent Application Publication No. 2006-341740 includes straps (tethers) provided in an airbag and that control the inflation. The straps each include a piece of base fabric having excellent stretchability, and a fiber member having a lower stretchability than the piece of base fabric. If the tensile force is small, the stretching of the strap is regulated by the fiber member. If the tensile force is large, the fiber member breaks and the piece of base fabric stretches with its stretchability.
An airbag device disclosed by Japenese Unexamined Patent Application Publication No. 07-277124 includes tethers connected to a bottom wall portion and to a top wall portion and that regulate the shape of inflation. The tethers are of two kinds: long and short ones. The long tether is for regulating the shape at the completion of the inflation. The short tether has a lower strength than the long tether and is connected to the bottom wall portion and to the top wall portion. When the airbag starts to be inflated and deployed, the short tether is first stretched. Accordingly, the distance between the bottom wall portion and the top wall portion is regulated, whereby the amount of projection of the airbag is regulated. Subsequently, the short tether breaks while the long tether is stretched, whereby the airbag is regulated to have a predetermined shape.
An airbag device disclosed by Japenese Patent No. 2677951 includes an inflation controlling member (tether) that controls the shape of an airbag. The inflation controlling member includes a releasable connected portion and an extendable portion. In an early stage of an inflation process, the releasable connected portion remains as it is while the inflation controlling member is extended to have an initial length. In an intermediate stage of the inflation process, the releasable connected portion is released, whereby the inflation controlling member is extended to have an intermediate length. In the final stage of the inflation process, the extendable portion is extended, whereby the inflation controlling member is extended to have a final length.
An airbag device disclosed by Japanese Unexamined Patent Application Publication No. 2003-095047 includes a tether that regulates the shape of inflation of an airbag. The tether includes a folded portion folded such that the tether is doubled, and a temporarily tacked portion (extension-amount-changeable means) where part of the doubled portion is tacked such that the tack is released when the internal pressure of the airbag exceeds a predetermined value. When the airbag starts to be inflated and deployed, the tether acts to retain the airbag to be in a first inflated state. When the internal pressure of the airbag exceeds the predetermined value, the tether acts to change the state of the airbag into a second inflated state.
An airbag device disclosed by Japanese Patent No. 4666059 includes opening-degree-changing means that changes the area of opening of a vent hole. The opening-degree-changing means includes a valve member and a tether. The valve member is capable of opening and closing the vent hole. The tether is connected at one end thereof to the valve member on the outside of the airbag and is also connected at the other end thereof to a top part of a piece of base fabric of the airbag that faces the occupant. When the airbag is deployed, the tether is stretched in the vertical direction of the vehicle in side view of the vehicle and urges the valve member in a closing direction. The tether acts as follows. In a state where the airbag has been completely inflated and deployed, the tether pulls the valve member in such a manner as to close the vent hole. When the occupant comes into contact with the airbag, the tether is loosened and acts to open the vent hole.